I have an issue with an mkv file in FCP. In VLC, the file plays perfectly, no pops or anything, but in FCP I get a popping, both in the viewer and canvas. I tried changing the audio rate to 41 khz...nothing. I tried some crossfades...nothing. The popping isn't as intermittent and regular as 41khz/44khz issues that I've had in prior projects, and this popping occurs within clips, not just at the beginnings or ends. Nothing looks out of the ordinary in the audio waveform. I've also tried rendering only as mixdown. Nope.
6 audio mono tracks,
32 bit floating point audio format
FCP should only ever have aif or wav uncompresed PCM audio at 48khz, 16 or 24 bit. It doesn't like anything else. All audio should be converted from various codecs to these two choices before they are imported into FCP and put in a timeline. Do it now before it gets uglier.